Influence of landscape retention capacity upon flood processes in Jičínka river basin

191 ACTA UNIVERSITATIS AGRICULTURAE ET SILVICULTURAE MENDELIANAE BRUNENSIS Volume 62 21 Number 1, 2014 http://dx.doi.org/10.11118/actaun201462010191 INFLUENCE OF LANDSCAPE RETENTION CAPACITY UPON FLOOD PROCESSES IN JIČÍNKA RIVER BASIN František Pavlík1, Miroslav Dumbrovský1 Abstract 1 Institute of Landscape Water Management, Faculty of Civil Engineering, Brno University of Technology, Veveří 95, 602 00 Brno, Czech Republic PAVLÍK FRANTIŠEK, DUMBROVSKÝ MIROSLAV. 2014. Infl uence of Landscape Retention Capacity Upon Flood Processes in Jičínka River Basin. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 62(1): 191–199. In a survey of landscape retention capability results of measurements obtained during the disastrous fl ood in June 2009 were used. The original method based on the balance among the daily precipitation fallen on the basin with discharges in the fi nal profi le was used on the analogy with transformation of the fl ood discharge through a reservoir. Following basin retention are defi ned: dynamic Rd, static Rs including the underground retention Rug and evaporation E, and total Rt. Main principal criteria were the eff ective static retention of the basin Rsef and a coeffi cient of the eff ective static basin retention sef (3). The coeffi cient of reducing fl ood culmination cul (4) was calculated, too. Also investigated factors having the most infl uence on a retention capacity of a basin are introduced. Summary of results are shown in the Tab. I. Values of the most important criterion quantities are marked in shadow colour. The results show, for example, that the found out coeffi cient sef is 0.52. It means that the soil (and slightly a vapour, too) in the basin caught 52% of volume of wave in the time of culmination discharge in a basin. Also some further interested fi ndings are introduced in the results and conclusions. Keywords: landscape, retention, fl ood fl ows, river basin INTRODUCTION During the June, 2009 the Czech Republic was suff ered by destructive fl oods. Regions of the Northern Moravia and parts of the North and Southwest Bohemia were seriously damaged. Flows o en higher than centenary ones killed a several peoples, and made huge economical damages, indeed. Such an event is therefore calling for a radical solution, aiming at reduction, eventually at the elimination of catastrophic impacts of such extreme climatic phenomena. The specialists from the water management range and the specialists for nature conservation are still discussing how to protect the landscape against fl oods in an optimal way (Prudký, Spitz, 2003). The principal problem is whether to prefer a construction of new reservoirs, eventually a reconstruction of the existing ones, or to increase a retention capacity of the landscape. Methods of a modifi cation of the fl ood fl ows using the retention capacity of the reservoir’s space (dams, ponds, polders, inundation) are more or less known, while methods of estimation of a landscape retention at the extremely high precipitation are not developed enough, therefore the appropriate quantitative data are missing about it (Spitz, Dumbrovský, Podhrázská, 2000). Our contribution is therefore aiming at the way of obtaining the proper data to estimate a retention capacity of the landscape during fl oods, and its application for Jičínka river basin. It was affl icted by fl oods due to the short term extreme precipitation, failing in the evening 24 th of June, 2009. The contribution is summing up a knowledge and investigation gained at the solution problems mentioned above at the study, prepared by Dumbrovský et al. (1998) within the government project „Evaluation of the fl ood situation July, 1997“. MATERIALS AND METHODS A method used contains of two parts: an approach to the quantitative evaluation of the retention 192 František Pavlík, Miroslav Dumbrovský ability of the landscape within a basin, and the way of quantifi cation of factors infl uencing a retention capacity of a basin. Quantifi cation of the retention capacity of a basin A retention capacity of the landscape was investigated for the entire basin by balancing hourly precipitation falls at the basin, and fl ows at the fi nal profi le. A basic principle of the balance approach is at the analogy of fi lling and evacuation of the retention space of the water reservoirs during the transformation of a fl ood fl ow through the resevoir, considering, that the total water retention Rt contains of four principal components (Spitz, Prudký, 2000): • surface retention Rsf, • hypodermic retention Rhd containing the subsurface water moving with subsurface water bearing layers, • underground retention Rug containing of a water caught at capillaries of the not saturated soil zones, and of a gravitation infi ltrated water, increasing the reserve of the underground water, • evapotranspiration E, i.e. a transpiration from the land surface, together with a transpiration by plants, and interception, i.e. a part of water remaining on the surface of plants. The used method of determining the retention capacity of the basin is also based on the separation of components of runoff , which dealt many of authors (Kulhavý et al., 2001). In this article has been applied method of analysis of subsidence branch, which dealt in detail for example Slepička et al., 1989; Kněžek, Kessl, 2000, or Serrano, 1997. During fl ood duration the volume of the underground retention and of evapotranspiration is changing much slower than volumes of the surface, and hypodermic retention. A sum of these retentions is therefore called a dynamic retention Rd. A sum of the underground retention and of an evapotranspiration is called the static retention Rs (Chow Ven Te, 1964). A division of the total basin retention Rt to the individual components is shown in the Fig 1. A relation between the instantaneous total basin retention, a sum of the hourly precipitation ∑Hi and a sum of the hourly fl ow off ∑Qi during a time interval of i-hours since a beginning of a fl ood may be expressed by the following equation: ti i i ii RHQ  , (1) while Rti = Rdi + Rsi . (2) From the hourly evaluation of data it is therefore possible at the every hour, or for a given time interval to quantify a total retention of a basin Rci, incl. its dynamic Rdi, and static Rsi components. From the point of view of the retention evaluation at the time of a fl ood, a maximum value of the instantaneous Rti is most important, which decrease the precipitation peak. The value was called the effi cient total basin retention Rtef, and its components are similarly called the effi cient dynamic basin retention Rdef, and an effi cient static basin retention Rsef. The effi cient total basin retention is taking place usually at the maximal instantaneous (at our case the hourly one) total fl ow off of the basin (surface fl ow off + hypodermic + underground ones) at the fi nal profi le. To be able to compare basin researched, the coeffi cients of retention have been established, i.e. the effi cient values of a retention were compared 1: Diagram of the distribution of total retention capacity of a basin Rt to the individual components Infl uence of Landscape Retention Capacity Upon Flood Processes in Jičínka River Basin 193 with the volume of the fl ood wave (i.e. a sum of the precipitation amount Hi from the fi rst to last, generally to the n-th hour), which initiated the fl ood. For instance, a coeffi cient of the effi cient static basin retention sef: is: 1 sef sef n i i R H     . (3) Similarly a coeffi cient of the effi cient dynamic basin retention def, and a coeffi cient of the total basin retention tef were established. The other important characteristics of a fl ood are a maximum hourly precipitation Hmax, and a maximum hourly fl ow Qmax. It was therefore established a coeffi cient of a decrease of the fl ood culmination cul, expressing a decrease of the precipitation fl ood peak, due to the total effi cient basin retention: max max kul Q H   . (4) Since we had hourly amounts of precipitation, and fl ow fl oods at our disposal only, we couldn’t evaluate time retardation between of maximum fl ow and maximum precipitation. Since the paper is aiming at the evaluation a landscape retention capacity during the fl ood, i.e. to estimate a part of a fl ood precipitation a basin is able to retain without damages, and to relieve out, (i.e. there was necessary to estimate a part of the fl ood precipitation caught by a soil and by a vapour), the principal criteria was the effi cient static retention Rsef, and a coeffi cient of the effi cient static retention sef. Quantifi cation of principal factors aff ecting the retention capacity of a basin Retention ability of the basin depends on many factors such as: geological structure, type of soil, topographic conditions, natural and hydrographic net (Mioduszewski, 1998). At Jičínka river basin the factors were evaluated, affl icting a retention basin capacity. These important factors were: a) land areas according to the way of land use and built-up area, b) geo-morphologic conditions characterised by an average slope of a basin, c) hydrologic soil conditions of the agricultural land, divided into 4 groups, A-D, according to a speed of infi ltration, i.e.: A – soils with a high speed of infi ltration, higher than 0.12 mm.min−1, B – soils with a middle speed of infi ltration from 0.06 to o.12 mm.min−1, C – soils with a low speed of infi ltration from 0.02 to 0.06 mm.min−1, D – soils with the very low speed of infi ltration, less than 0.02 mm.min−1. d) hydrogeology conditions of a subsoil, e) shape of the basin, characterised by the dimensionless coeffi cient , taking in account a size of a basin F, and a length of a fl ow valley L, estimated according to the relation: 2 F L  , (5) which expresses a relation between an average width of a basin, and a length of the fl ow valley; a coeffi cient  has a value less than 0.25 for a fan-shaped basins, and larger than 0.25 for an oblong shaped basins, f) an average soil moisture before a fl ood precipitation, evaluated by the antecedent precipitation index, marked as API including a parameter of the declination k < 1, (experimental values of which range from 0.85 to 0.98), and a value Pt of the precipitation lasted t days, at our case 5 days before a start of the fl ood precipitation, according to a relation: 1 tt tt API P k . (6) These above factors were determined primarily using the tools of ArcGis 9.3. For determine characteristics of streams and their basins were used as the basis database DIBAVOD (Source: TGM WRI), land use layer was prepared combination of digital data layers LPIS and own fi eld reconnaissance a er the fl ood. Hydropedologic soil properties were derived from the digital soil layer of estimated pedologic-ecological unit. For the processing of hydrological and climatological calculations were used standard tools of Microso Excel 2007. RESULTS Analysis of contributing factors Runoff and retention rates in Jičínka river basin by fl ood in June 2009, is infl uenced by complex of factors, climatic, hydrological, hydropedologic, factor of vegetation (land use) and morphology. Vegetation cover Representation of land use (Fig. 2) is an important aspect for retention and runoff conditions in the river basin, and land use is the only factor that can be aff ected by human activities directly. Crucial to the formation of runoff processes were representative of the current crops. In this case representation of erosive dangerous plants (Fig. 3) was fortunately low. The higher proportion of wide-row crops in the river basin it can be assumed even more serious consequences of fl ood. Morphological conditions Further important factor that signifi cantly aff ects the characteristics of runoff and retention capacity is 194 František Pavlík, Miroslav Dumbrovský slope. Conditions of the area are shown in the Tab. I. In the Jičínka river basin is average of slope 13.2%. Hydrological conditions Conditions of the area are shown in the Fig. 4. Climatic conditions The primary cause of fl ood in the Jičínka river basin was as a rainfall in the evening of 24. 6. 2009, which reached maximum intensity between 19 and 22 hours according to local residents, so the 2: Land Use during flood situation 3: Crops during flood situation I: Morfological characteristics of a catchment Slope category Spatial representation of category [%] 0–5% 25.2 5–10% 25.6 10–15% 16.6 15–20% 10.9 20–30% 12.3 nad 30% 9.4 Infl uence of Landscape Retention Capacity Upon Flood Processes in Jičínka River Basin 195 4: Hydrological network 5: Distribution of precipitation during flood situation 196 František Pavlík, Miroslav Dumbrovský rainfall in the previous fi ve days, which reached 24th hour precipitation on average 20 mm (source: measurements of local users). In the Fig. 5 is shown the spatial distribution of data on the distribution of causal precipitation of 24. 6. 2009 (source: Czech Hydrometeorological Institute). Hydropedologic conditions An important factor which greatly infl uenced the retention capacity of river basin and characteristics of direct runoff is represented by a high percentage of type of soils with low intensity of infi ltration. Hydrologic soil groups (HSG) “C” and “D” type represent approximately 50% of the area of Jičínka river basin (Tab. II). The primary cause of fl ooding in the Jičínka basin was torrential rainfall in the evening of 24th June 2009 (according to local people reached maximum intensity between 19 and 22 hours) and rainfall in the previous fi ve days, which reached an average 24 hour precipitation about 20 mm. Basic physicalgeographical characteristics of the watershed are shown in Tab. II. For river basin was evaluated the hourly amounts of precipitation fallen at the basin, and fl ows at the fi nal profi le from the 22th of June to the 5th of July were evaluated by a tabulation and graphically, incl. their cumulative values. A cumulative curve of diff erences is given at a graph in the Fig. 6, presenting an instantaneous retention of the basin every hour of the observed period followed. (See the upper curve at the Fig. 6). The dynamic and static retention were discriminated according to following rules: a) since a beginning of a fl ood period (i.e. since the 22th of June, 2009 the gravitation, and capillary pores were fi lled at not saturated soil layers till a hour, when a fl ow increased substantially, and since that moment a surface, i.e. dynamic retention (started at the Fig. 6 the phenomenon is represented by diff erences between dashed and full lines) and the water further infi ltrated also into gravitation voids at a constant rate hourly into the underground water, b) a hour of the end of a dynamic (surface) retention was established at the descending line of hourly fl ows, when a hourly fl ow sharply decreased, while the static retention reached maximum, and its evacuation due to the underground fl ow started, c) at a graph of an instantaneous total retention a boundary line between a dynamic and static retention is linear, resulting from the assumed constant hourly growth of a static retention connecting points of a beginning and of an end of dynamic retention; from this point a curve continues expressing a decrease of the static retention (a course of the static retention at the Fig. 6 is shown in full line), d) process of the evacuation of a static retention continued later on, a fl ood episode could be 6: Diagram of the distribution of total retention capacity of a basin Rt to the individual components Infl uence of Landscape Retention Capacity Upon Flood Processes in Jičínka River Basin 197 considered as fi nished, when a value of the hourly fl ow approached to a starting value again, or is determined the contractual of the fl oods as in our case. Results of the basin evaluated are presented at the Tab. II. Basic identifi cation data about basin considered are given at a heading of a Tab. II, while values observed are included at the table itself. Values of the most important hydrological data for an estimation of the basin retention, i.e. concerning the static basin retention, and the decrease of a fl ood culmination, are introduced in the Tab. II. Results show, that a coeffi cient of effi cient static retention reaches value of 0.52, i.e. the soil retained about 52% of the wave volume at a time of the outfl ow culmination. This volume is slightly higher than dynamic effi cient retention (including a surface, and hypodermic water), being at value of 34%. A coeffi cient of the total effi cient basin retention reaches value of 86% from the volume of the fl ood wave. A coeffi cient of the decrease of a fl ood culmination reaches value of 24%. CONCLUSIONS Findings, gathered during the research of the retention of the Jičínka river basin during the 2009 fl oods, can be summarised into the following conclusions: a) A proposed balance method used which is based upon the evaluation of hourly precipitation and fl ows at the time of fl ooding, showed suitable for the study of the quantitative analysis of the retention basin capacity. b) To improve a reliability of the balance method there is necessary to have the more detailed information about the precipitation, and fl ows at the beginning of a fl ood, for instance an 15 minutes values, as well as values of the fl ood fl ow volumes, and estimated values of the underground water variation, values of II: Summary of data found out in the investigation of the river Jičínka basin in the June fl ood 2009 Final profi le Nový Jičín Flow Jičínka Area of the basin F [km2] 93.9 Length of fl ow L [km] 17.7 Volume of fl ood precipitation [mil.m3] ∑Hi12.74 [mm] 135.7 Effi cient static retention Rsef [mil.m3] 6.65 [mm] 70.8 Effi cient dynamic retention Rdef [mil.m3] 4.28 [mm] 45.6 Effi cient total retention Rcef [mil.m3] 10.93 [mm] 116.4 Coeffi cient of the effi cient static retention sef 0.52 Coeffi cient of the effi cient dynamic retention def 0.34 Coeffi cient of the effi cient total retention cef 0.86 Maximum hourly fl ow Qmax [mil.m3] 0.95 [m3.s−1] 263.5 Maximum hourly precipitation Hmax [mil.m3] 3.89 [mm] 41.2 Coeffi cient of the decrease of fl ood culminatin kul 0.24 Average inclination of river basin [% ] 13.2 Average soil moisture before a fl ood precipitation API [mm] 20.0 Shape of the basin 0.30 Hydrol. soil group according to a speed infi ltration [mm.min−1] A: > 0.012 B: 0.06–0.12 C: 0.02–0.06 D: < 0.02 Agr. land A [km2] [% of the basin area] 4.8 5.1 B [km2] [% of the basin area] 40 42.6 C [km2] [% of the basin area ] 22.1 23.5 D [km2] [% of the basin area] 27.0 28.8 198 František Pavlík, Miroslav Dumbrovský transpiration, and of the soil moisture before the start of fl ooding. c) Ascertained value of the static basin retention is 52% of the volume of fl ood precipitation, being at the level of the dynamic retention values that was 34%. d) Basin decreased the culminant hourly precipitation to the value of a culmination fl ow, which was equal to 24% of the top hourly precipitation. Estimated values of hydrology quantities are unique, since such a fl ood phenomena are rare and are poorly documented at the Czech Republic. The method described can be used even as a base for evaluation of the appropriate measures to increase the landscape retention capacity. Method can be used for evaluation of fl ash fl ooding, but also for evaluation of regional precipitation fl oods. The obtained results are consistent with the results of Kuráž (1999). The authors describe transformation quantitative capacity of the soil in the rainfallrunoff relationship. As an indicator criteria were selected Hydrologic soil groups, which indicates the soil’s ability to transform precipitation and implicitly includes the ability to redistribute land soil moisture. Transformation quantitative soil functions is given by the depth of the soil profi le, hydrophysical characteristics of soils, vegetation cover (type and condition). The fi ndings also confi rm the results of research of other authors (Dumbrovský et al., 1998; Spitz et al., 2000; Prudký, 2001; Mašíček, 2010). Reduced water retention capacity in the watershed due to decreased water retention capacity of soils, inappropriate Land Use and Land cover in the basin and the presence of elements increase surface runoff . The negative eff ect is amplifi ed in the case of saturation of soils in the catchment during the period of extreme precipitation. SUMMARY This paper describes the retention capacity of the river basin and its course during a fl ash fl ood. Retention capacity of the river basin was measured of balancing of precipitation fallen in the river basin and discharges in the fi nal profi le. For determine the retention characteristics of the river basin was used method, which balances precipitation and runoff in the time step (in our case was used hourly balancing step). The method is based on the theory of separation of components of runoff and also used the analogy with transformation of the fl ood discharge through a reservoir. In the solved river basin were assessed factors that most infl uence the retention capacity of the river basin. Processing and analysis of data showed the infl uence of various causal factors on the individual components of retention capacity. Retention capacity of river basin during fl ood episode is a dynamic characteristic that is infl uenced by many parameters related to the physical-geographic factors of river basin. On the basis of past performance and validation, it can be stated that the method appears to be an ideal tool for evaluating the retention capacity of the river basin, as well as to evaluate the eff ectiveness of protective measures. The applied method of balancing is very transparency and it is not diffi cult on the input data that can be obtained from Czech hydrometeorological institute (CHMI) or by own measurements or modeled. The disadvantage of the method is its partial subjectivity. Acknowledgement The paper was elaborated with fi nancial support from Research Project MZE QJ1230066 and QJ1320157 thanks to the support of the Ministry of Agriculture of the Czech Republic. REFERENCES DUMBROVSKÝ, M. et al., 1998: Analysis of Retention Potential of the Opava River Basin with an Analysis of the Structure and the Area Dislocation of Cultures (in Czech). Research Report. Research Institute of Soil and Water Conservation, Prague, 25 p. CHOW VEN TE, 1964: Handbook of Applied Hydrology. New York: Mc Graw – Hill Book Company New York . MAŠÍCEK, T., 2010: Retention potential of Fryšávka river basin. Ph.D Thessis. Brno: Mendel University Brno. 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SPITZ, P., PRUDKÝ, J., 2000: Methodology for calculating the retention capacity of the catchment during fl oods. User output of the project NAZV EP 9153 Evaluation of water retention capacity of soils and landscapes during fl oods and possibilities of its increasing. Praha: VÚMOP Praha, 19 s., 10 supplements. Contact information František Pavlík: [email protected] Miroslav Dumbrovský: [email protected]